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Triangular Benzene Sandwiches

Electron-rich species such as benzene can interact with low-lying unoccupied orbitals of metal centers, for instance, when benzene adsorbs on metal surfaces. Mercury cations and organomercurials are known to have high affinity for arenes. Tsunoda and Gabbai have modeled such surface interactions with the compound 1, which contains three mercury atoms bridged by fluorophenylene groups. Boiling 1 in benzene yields a supramolecular complex whose crystal structure reveals stacks of benzene molecules alternating with 1 in staggered fashion. Each mercury atom interacts with a p bond of benzene in an “η2” fashion (an orbital from the mercury atom points into a π bond). The interaction is highly symmetrical in that the benzene molecules are undistorted; it is also weak, in that the C-C bond lengths in benzene remain unchanged. — PDS